IE8 will by default render pages in standard mode but you have the option of using Compatibility View to render the page in an emulated IE7 mode. The new thing now is that you can subscribe on a list of websites that should be rendered in Compatibility mode, and if enough people select Compatibility View for a website it will end up on the list and after an update you also will render this page in Compatibility View. Of course this feature is already enabled if you use “Default install” of IE8, so most people will probably never change this.